In high electron mobility transistors (HEMTs) using a group III-V compound semiconductor, a two-dimensional electron gas (2DEG) is formed in a channel layer. The two-dimensional electron gas helps to allow for low on-state resistance and a high switching speed.
In the off-state of such a HEMT, a high voltage can be applied between a source electrode and a drain electrode, and leaked electrons are caused to flow into the drain electrode. At that time, some of the electrons can be trapped in an interface between a semiconductor layer and an insulation layer, or inside the insulation layer, and become a negative fixed charge. Because of the negative fixed charge, channel depletion occurs in an on state of the HEMT, and this may cause an increase in on-state resistance. Such a phenomenon is called current collapse.
Thus it may be desirable to prevent trapping of electrons and suppress current collapse.